*extendsfdf2_1_sse_only): Unify enable constraint with
respect to TARGET_SSE2, TARGET_80387, TARGET_SSE_MATH
and TARGET_MIX_SSE_I387.
(*extendsfdf2_i387): New insn pattern.
(*extendsfdf2_1): Rename to *extendsfdf2_mixed. Fix
register constraint for operand 0.
(*extendsfdf2_1_sse_only): Rename to *extendsfdf2_sse.
(*extend{s,d}fxf2_1): Rename to *extend{s,d}fxf2_i387.